Transmission of synchronization and control signals in a broadband wireless system

ABSTRACT

In a broadband wireless communication system, a primary control signal may be relocated within the operation band for transmission while avoiding interference. For example, if the primary control signal employs P contiguous sub carriers, the primary control signal can be placed in any section of the band that has P contiguous subcarriers. If a narrow-band interferer appears at one end of the band, the primary control signals can be placed at the other end. If the interferer appears in the middle, the primary can be relocated to either end of the band. The placement of primary control signals can be changed as the interference environment changes.

CROSS-REFERENCE

This application claims the priority of U.S. Provisional Application No.61/455,986 entitled Methods and Apparatus for Transmission ofSynchronization and Control Signals in a Broadband Wireless System,filed Oct. 29, 2010, which is hereby incorporated by reference in itsentirety.

TECHNICAL FIELD

The disclosed embodiments relate, in general, to wireless or wire-linecommunications and include methods and apparatus for transmission ofsynchronization and control signals, although these are merely exemplaryand non-limiting fields.

BACKGROUND

In an LTE system, the synchronization (SYNC) signals and thebroadcasting signals on the physical broadcast channel (PBCH) occupy arelatively narrow bandwidth (1.08 MHz) and are fixed at the center ofthe operation channel of a much wider bandwidth. The SYNC signals andinformation carried on the PBCH are crucial to system operation. TheSYNC signals, generated based on Zadoff-Chu sequences, enable a mobilestation to find the base station of the cell that the mobile station isin and to synchronize with the network. The PBCH carries critical systemcontrol information that a mobile needs to access the network. Since LTEis designed for use on a licensed spectrum, there is no need to considerinterference originated from other systems (i.e., no inter-systeminterference). In this case, the fixed-location design of SYNC signalsand PBCH is sufficient for the operation of the system.

Recently, the premium spectrum bands have been opened up by regulatorsfor unlicensed use, especially TV channels that are now available due toswitching from analogue to digital TV broadcasting. In an unlicensedenvironment, there may be considerably more interference from varioussources. When used in such an environment, the fixed-location design ofSYNC signals and PBCH such as in an LTE system may not cope well withinterference. The SYNC signals and PBCH may be vulnerable in cases wherea narrow-band interferer is present where the SYNC signals and PBCH arein frequency, as depicted in FIG. 1. As a result, performance of thesystem may be greatly degraded.

SUMMARY

In accordance with various embodiments of the present invention, in abroadband wireless communication system, a primary control signal can berelocated within the operation band for transmission while avoidinginterference. For example, if the primary control signal employs Pcontiguous subcarriers, the primary control signal can be placed in anysection of the band that has P contiguous subcarriers. If a narrow-handinterferer appears at one end of the band, the primary control signalscan be placed at the other end. If the interferer appears in the middle,the primary can be relocated to either end of the band. The placement ofprimary control signals can be changed as the interference environmentchanges; that is, the relocation of a primary control signal can beadaptive to interference environment.

BRIEF DESCRIPTION OF THE DRAWINGS

The systems, methods, and computer readable media for communicating in awireless communications system in accordance with this specification arefurther described with reference to the accompanying drawings in which:

FIG. 1 depicts, using frequency, a scenario in which a narrow-handinterferer appears where the SYNC signals and PBCH are located.

FIG. 2 depicts a representative diagram of a wireless communicationsystem with a control server, a content server, a backbone network, basestations (BS) and mobile stations (MS).

FIG. 3 is a graphical depiction of a typical radio frame structure inthe time domain.

FIG. 4 depicts a representation of a time-frequency resources blockconsisting of multiple subcarriers in multiple consecutive symbols.

FIG. 5 is a block diagram of a typical mobile detection process in abroadband wireless communication system.

FIG. 6 is a block diagram of a representative transmitter used at thebase station for transmitting a SYNC or a PBCH.

FIG. 7 is a block diagram of a representative receiver used at themobile station for receiving a SYNC or a PBCH.

FIG. 8 is graphical depictions of a primary control signal relocated toavoid interference.

FIG. 9 is graphical depictions of PSS, SSS, and PBCH aligned infrequency.

FIG. 10 is a graphical depiction of non-overlap subbands in frequency.

FIG. 11 is a graphical depiction of multiple PSS, SSS, and PBCH beingtransmitted using a set of subbands.

FIG. 12 is a graphical depiction of a bitmap that is used to indicatewhich frequency resources are usable or unusable.

FIG. 13 is a block diagram of representative receiving processes fordetection of a SYNC.

FIG. 14 is a block diagram of another representative receiving processfor detection of a SYNC.

FIG. 15 illustrates an example of an operational procedure forpracticing aspects of the present disclosure.

FIG. 16 illustrates an example of an operational procedure forpracticing aspects of the present disclosure.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Certain specific details are set forth in the following description andfigures to provide a thorough understanding of various embodiments ofthe disclosure. Certain well-known details often associated withcomputing and software technology are not set forth in the followingdisclosure to avoid unnecessarily obscuring the various embodiments ofthe disclosure. Further, those of ordinary skill in the relevant artwill understand that they can practice other embodiments of thedisclosure without one or more of the details described below. Finally,while various methods are described with reference to steps andsequences in the following disclosure, the description as such is forproviding a clear implementation of embodiments of the disclosure, andthe steps and sequences of steps should not be taken as required topractice this disclosure.

The terminology used in the description presented below is intended tobe interpreted in its broadest reasonable manner, even though it isbeing used in conjunction with a detailed description of certainspecific embodiments of the invention. Certain terms may even beemphasized below; however, any terminology intended to be interpreted inany restricted manner will be overtly and specifically defined as suchin this Detailed Description section.

It should be understood that the various techniques described herein mayhe implemented in connection with hardware or software or, whereappropriate, with a combination of both. Thus, the methods and apparatusof the disclosure, or certain aspects or portions thereof, may take theform of program code (i.e., instructions) embodied in tangible media,such as floppy diskettes, CD-ROMs, hard drives, or any othermachine-readable storage medium wherein, when the program code is loadedinto and executed by a machine, such as a computer, the machine becomesan apparatus for practicing the disclosure. In the case of program codeexecution on programmable computers, the computing device generallyincludes a processor, a storage medium readable by the processor(including volatile and non-volatile memory and/or storage elements), atleast one input device, and at least one output device. One or moreprograms that may implement or utilize the processes described inconnection with the disclosure, e.g., through the use of an applicationprogramming interface (API), reusable controls, or the like. Suchprograms are preferably implemented in a high level procedural or objectoriented programming language to communicate with a computer system.However, the program(s) can be implemented in assembly or machinelanguage, if desired. In any case, the language may be a compiled orinterpreted language, and combined with hardware implementations.

Some of the embodiments described herein describe methods and systemsfor flexible frequency-division duplex (FFDD) transmission. The methodsand systems may also be combined with a traditional TDD or FDD system tocreate a hybrid system. The multiple access technology mentioned hereincan be of any special format such as Code Division Multiple Access(CDMA), Time Division Multiple Access (TDMA), Frequency DivisionMultiple Access (FDMA), Orthogonal Frequency Division Multiple Access(OFDMA), Multi-Carrier Code Division Multiple Access (MC-CDMA), orCarrier Sensing Multiple Access (CSMA).

Without loss of generality, OFDMA is employed herein as an example toillustrate different aspects of these embodiments.

FIG. 1 is a representative diagram of a wireless communication systemwith base stations (BS) 140 and mobile stations (MS) 150. A controlserver (CS) 120 controls one or multiple base stations (BS). Controlserver 120 is connected to the base stations via the backbone network110. Control server 120 coordinates multimedia content broadcast,including terrestrial/mobile TV, for example, via a single frequencynetwork (SFN) and cellular data unicast, such as voice-over-LP andinternet traffic. In some embodiments, backbone network 110 is a packetdata network that can either be a wired or a wireless network. Backbonenetwork 110 may also connect to other servers in the system, such asmultimedia content servers 130 and network management servers.

The geographic region serviced by the system may be divided into aplurality of cells, and wireless coverage may be provided in each cellby a base station. One or more mobile devices may be fixed or may roamwithin the geographic region. The mobile devices may be used as aninterface between users and the network. A base station may serve as afocal point to transmit information to and receive information from themobile devices within the cell that it serves by radio signals. A basestation may be a macro-station that covers a large geographical area ora macro-cell, a micro or pico station that covers a small area or amicro/pico-cell, or a femto station that typically covers an indoor areaor a femtocell. Those skilled in the art will appreciate that if a cellis divided into sectors, each sector can be considered a cell. In thiscontext, the terms “cell” and “sector” are interchangeable.

The transmission from a base station to a mobile station may be called adownlink (DL) and the transmission from a mobile station to a basestation may be called an uplink (UL). The transmission may take placewithin a frequency range extending between two limiting frequencies.This range of frequency resource may be defined as an operatingfrequency band/channel or simply band in this text. The center of thefrequency range is typically the center frequency or carrier frequencyand the span of the frequency range is normally referred to as thebandwidth. For example, the frequency band for Broadcast Channel 36 inthe United States is centered at 605 MHz with a bandwidth of 6 MHz. Inanother example, a 3GPP WCDMA system may use a 5 MHz DL band and a 5 MHzUL band.

FIG. 2 is a representative diagram of a wireless communication systemwith base stations (BS) and mobile stations (MS). There is a controlserver (CS) that controls one or multiple base stations (BS). Thecontrol server is connected to the base stations via the backbonenetwork. It coordinates multimedia content broadcast, includingterrestrial/mobile TV, for example, via a single frequency network (SFN)and cellular data unicast, such as voice-over-LP and internet traffic.In the presently disclosed embodiments, the backbone network may be apacket data network that can either be a wired or a wireless network.The backbone network may also connect to other servers in the system,such as multimedia content servers and network management servers.

The geographic region serviced by the system may be divided into aplurality of cells, and wireless coverage may be provided in each cellby a base station. One or more mobile devices may be fixed or may roamwithin the geographic region. The mobile devices may be used as aninterface between users and the network. A base station may serve as afocal point to transmit information to and receive information from themobile devices within the cell that it serves by radio signals. A basestation may be a macro-station that covers a large geographical area ora macro-cell, a micro or pico station that covers a small area or amicro/pico-cell, or a femto station that typically covers an indoor areaor a femtocell. Those skilled in the art will appreciate that if a cellis divided into sectors, from a system engineering point of view eachsector can be considered as a cell. In this context, the terms “cell”and “sector” are interchangeable.

The transmission from a base station to a mobile station is called adownlink (DL) and the transmission from a mobile station to a basestation is called an uplink (UL). The transmission takes place within afrequency range extending between two limiting frequencies. This rangeof frequency resource is defined as an operating frequency band/channelor simply band in this text. The center of the frequency range isusually called the center frequency or carrier frequency and the span ofthe frequency range is normally referred to as the bandwidth.

The wireless communication system may use a certain radio framestructure to facilitate the transmission. For example, a radio frame mayconsist of multiple (L) subframes and each subframe may comprisemultiple (M) OFDM symbols, as shown in FIG. 3. In some embodiments,multiple (K) frames may form a super frame. In other embodiments, asubframe may be further divided into multiple time slots and each slotmay comprise multiple OFDM symbols. Those skilled in the art willappreciate that the division of radio frames and its granularity are tofacilitate radio transmission. Other forms of division or othernomenclature may, of course, be used depending on the requirements ofthe communication system.

The OFDM time domain waveform is generated by applying theinverse-fast-Fourier-transform (IFFT) to the OFDM signals in thefrequency domain. A basic structure of a multi-carrier signal in thefrequency domain is made up of subcarriers, which can be modulated tocarry information data and reference signals. A copy of the last portionof the time waveform, known as the cyclic prefix (CP), is inserted atthe beginning of the waveform itself to form an OFDM symbol.

The basic structure of an OFDM signal in the frequency domain is made upof subcarriers. For a given bandwidth of a spectral band or channel, thenumber of usable subcarriers is finite and limited, the value of whichdepends on the size of the FFT and the sampling frequency and theeffective bandwidth. OFDM symbols and subcarriers can be arranged intotime-frequency resource blocks, each of which consists of multiplesubcarriers in multiple consecutive symbols as shown in FIG. 4, tosupport scalability and multiple-access. One or more resource blocks mayhe used to form a subchannel dedicated for control information or/anddata information.

In one embodiment, the same structure of the transmission frame may beused by all the cells within the system and frames may be transmitted insynchronization among the cells. Primary control signals such assynchronization signals and broadcasting signals on physical broadcastchannels may be transmitted using one or more OFDM symbols in a frame orsubframe.

In a broadband wireless communication system, a primary control signalis broadcasted from a base station to mobile stations. A primary controlsignal may be referred to as a preamble, synchronization signal,reference signal, header, broadcast control channel, or other terms inthe industry. Notwithstanding the nomenclature, its purpose is crucialto system operation. The primary control signal carries timing,frequency, cell identity, system parameter information, which enables amobile station to find the base station of the cell it is in, tosynchronize with the network, and to access to the network. In thefollowing, the terms “control signal” and “control channel” may be usedinterchangeably, whereas a control channel is used to carry theso-mentioned control signal and a control signal is carried in theso-mentioned control channel.

In some embodiments, the primary control signal comprises asynchronization signal (SYNC), which may be used by mobile stations forfunctions such as time synchronization, frequency synchronization, andcell identification. A SYNC may further comprise a primarysynchronization signal (PSS) and a secondary synchronization signal(SSS) for multi-step execution of the mobile functions. A SYNC can berealized using a direct sequence in the time or frequency domain. It issometimes transmitted in the beginning of a frame and hence it is alsoknown as a preamble. A SYNC may occupy only a fraction of the operationbandwidth. A SYNC can be placed at any frequency location within theoperating bandwidth to facilitate the system operation. In some cases,it may be fixed at a center subband or occupy another subband within theoperation bandwidth as detailed in ensuing descriptions. In oneembodiment, a SYNC signal has small autocorrelation sidelobes relativeto the peak of its autocorrelation and has small cross-correlation withother SYNC signals.

In other embodiments, the primary control signal further comprises abroadcasting signal that carries critical system information (e.g.,system operating bandwidth, system frame number, control channelstructure, and indication of usable frequency resources) over a physicalbroadcast channel (PBCH). A PB CH may consist of a set of contiguoussubcarriers, occupying only a fraction of the operation bandwidth. APBCH can be placed in any frequency location with the operatingbandwidth to facilitate the system operation. In some cases, it may befixed at a center subband or occupy another subband within the operationbandwidth as detailed in ensuing descriptions. Furthermore, a PBCH mayoccupy one or more consecutive symbols within a subframe/frame.

In further embodiments, a regular control channel comprises a pluralityof subcarriers, which can be located anywhere within the operatingbandwidth in the first few OFDM symbols within a subframe/frame. Aregular control channel is exclusively dedicated for carrying controlinformation. In contrast, a data channel comprises one or moretime-frequency resource blocks. The resource blocks are not necessarilycontiguous and can be located anywhere within the operating bandwidth. Adata channel is primarily used for carrying information data; however,it may be sometimes used to carry control information.

A typical mobile detection process in a broadband wireless communicationsystem is depicted by the block diagram in FIG. 5. To start with, amobile station scans for the signature and frequency location of a PSSover potential frequency bands. A mobile station synchronizes in timeand frequency with the system by detecting the primary and secondarysynchronization signals and derives essential information such as cellidentity. One way to detect whether there is a synchronization signal isto correlate the signal received at the mobile with a sequence stored atthe mobile station. A high peak relative to the sidelobe level in thecorrelation result indicates the presence of the synchronization signal.If the cell identity is embedded in the sequence, the correlation resultmay also reveal the cell identity. Subsequent to the detection, themobile station may obtain critical system information such as theoperating bandwidth, frame number, control channel structures, andinformation of usable frequency resources (subcarriers, resource blocks,macro blocks, or subbands) by decoding the signals carried in thephysical broadcast channel. It then extracts control information bydecoding the data carried in the regular control channels. Once themobile station has all the necessary control information, it is enabledto carry out normal communication with its serving bastion station. Inan embodiment, when a mobile station enters the network, it locks onto afrequency band according to design criteria, such as high signal powerlevel, high signal to interference/noise ratio (SINR), low traffic loador large available capacity, usable frequency resources indicated by PBCH bit map, or a combination thereof.

In a handoff process, which is used by a mobile station to transfer anongoing connection session from a (serving) cell to a (target) cell, amobile station may receive a neighbor advertisement message providingproper handoff information. Such information may reduce unnecessaryoverhead for scanning. If a handoff decision is made, the mobile stationperforms functions such as time and frequency synchronization, cellidentity detection, and decoding the PBCH for critical systeminformation such as the operating bandwidth, frame number, controlchannel structures, and information of usable frequency resources(subcarriers, resource blocks, macro blocks, or subbands). Subsequently,the mobile station establishes the link with the target base station andthen terminates the service by the original base station.

A control server may comprise components such as processors, memorybanks, switches, routers, and interfaces. Together, these componentsenable the server to perform necessary functions such as compressing anddecompressing packet headers, removing and adding packet headers,segmenting and concatenating packets, and managing databases.

FIG. 6 is a block diagram of a representative transmitter used at thebase station for transmitting a SYNC or a PBCH. The transmitter includescomponents such as a sequence generator, channel encoder and ratematcher, modulator, multiplexer, subcarrier mapper, inverse fast Fouriertransform (IFFT), and radio frequency (RF) transmitter. In the case ofSYNC transmission, information such as cell identity and timing is inputto the sequence generator to be embedded in a sequence. The elements ofa sequence are assigned to a set of subcarriers by the subcarriermapper, to which the IFFT is applied, resulting in a time-domain signalto be transmitted. In the case of PBCH transmission, control informationdata is encoded and matched to a particular rate. The encoded data areassigned to a set of subcarriers with a particular modulation, to whichthe IFFT is applied, resulting in a time-domain signal to betransmitted.

A controller, coupled with memory, controls the operation of thetransmitter. In particular, the controller also controls theconfiguration of the set of subcarriers used for SYNC or PB CH fortransmission. The configuration may include frequencies and powerlevels.

FIG. 7 is a block diagram of a representative receiver used at themobile station for receiving a SYNC or a PBCH. The receiver includescomponents such as an RF receiver, signal processor, fast Fouriertransform (FFT), demodulator, and decoder. In the case of SYNCreception, the received signals are input to the signal processor to beprocessed to extract the information embedded in the SYNC. The signalprocessor performs various basic mathematical functions and specialsignal processing functions such as low-pass filtering, band-passfiltering, transforms, matched filtering, and correlation. In the caseof PBCH reception, an FFT is applied to the received signals. Thesubcarriers corresponding to the PBCH are demodulated and decoded torecover the control information data.

A controller, coupled with memory, controls the operation of thereceiver. In particular, the controller also controls the configurationof the set of subcarriers used for SYNC or PBCH for reception.

Those skilled in the art will appreciate that these componentsconstruct, transmit, and receive a communication signal containing thedata. Other forms of transmitters or receivers may, of course, be useddepending on the requirements of the communication system.

In accordance with aspects of certain embodiments of the presentinvention, in a broadband wireless communication system, a primarycontrol signal can be relocated within the operation band fortransmission while avoiding interference. For example, if the primarycontrol signal employs P contiguous subcarriers, it can be placed in anysection of the band that has P contiguous subcarriers. If a narrow-bandinterferer appears at one end of the band, the primary control signalscan be placed at the other end. If the interferer appears in the middle,the primary control signals can be relocated to either end of the bandor each of the primary control signals can be divided into two portions,each portion relocated at one end of the band. The placement of primarycontrol signals can be changed as the interference environment changes;that is, the relocation of a primary control signal can be adaptive tointerference environment.

In one embodiment, the frequency location of the channel that carries aprimary control signal varies within the operating bandwidth indifferent cells or geo-locations in the system. In another embodiment,such position variation of primary control channels depends at least inpart on the variation of interference (such as the strength andfrequency location) in the cells. The interference may compriseinter-system interference from, e.g., TV broadcasting signals, orintra-system interference from other cells.

In some embodiments, a primary control signal can be relocated in such away that its center subcarrier can be placed at any point within theoperation band to avoid interference, as depicted in FIG. 8. Forexample, in a system with a total of Q usable subcarriers within itsbandwidth, which are labeled by

$\left\{ {{- \frac{Q}{2}},{{- \frac{Q}{2}} + 1},\ldots \mspace{14mu},{- 1},0,1,{{\ldots \mspace{14mu} \frac{Q}{2}} - 1}} \right\}$

and Q is an even number, the center subcarrier of a primary controlsignal with P subcarriers can be placed at the frequency location(subcarrier index) f_(c), where

${{- \frac{Q}{2}} + \left\lfloor \frac{P}{2} \right\rfloor} < f_{c} < {\frac{Q}{2} - \left\lfloor \frac{P}{2} \right\rfloor}$

where └┘ represents the floor function or greatest integer operator.Guard subcarriers (zero energy) may be placed on both sides of theprimary control signal. In this case, if a total of S guard subcarriersare used, then

${{- \frac{Q}{2}} + \left\lfloor \frac{P + S}{2} \right\rfloor} < f_{c} < {\frac{Q}{2} - \left\lfloor \frac{P + S}{2} \right\rfloor}$

In one embodiment, the center subcarrier of a primary control signal mayonly be placed at a frequency location that is related to the systemparameters (e.g., clock rate, sampling rate, and subcarrier spacing) orsimply a predetermined frequency location. For example, the centersubcarrier of a primary control channel is placed at a position in thefrequency grids that are (positive and negative) multiples of a systemsampling rate/clock rate, a (positive and negative) fraction of thesampling rate/clock rate, or (positive and negative) multiples of asubcarrier spacing. For instance, the center frequency of a primarycontrol channel can be placed at ±3.84n MHz, where n is an integer. Forfurther example, the center subcarrier of a SYNC is placed at one of thefrequency locations f_(c)={0,±L_(sync),±2L_(sync),±3L_(sync), . . . },where L_(sync) denotes the length of the SYNC sequence.

In other embodiments, multiple primary control signals may occupy thesame frequency section in different OFDM symbols; that is, their centersubcarrier corresponds to the same subcarrier index. In an example shownin FIG. 9, PSS, SSS, and PBCH are aligned in frequency but placed indifferent OFDM symbols.

In further embodiments, a primary control signal may be relocated at afrequency location with a sufficient level of channel quality (e.g.,sufficiently high mean SNR or sufficiently low average level ofinterference) for mobile station to detect the primary control signal.The channel quality can be determined using various methods. In oneembodiment, mobile stations may survey the channel quality, based inpart on DL signals from their serving base stations, and feed therelevant information back to their serving base stations, which thenaggregate the information to determine the frequency location with asufficient level of channel quality. In another embodiment, basestations may survey the channel quality, based in part on UL signalsfrom their mobile stations, and determine the frequency location withsufficient channel quality.

In other embodiments, the transmission of primary control signals mayhop in frequency from one subframe, slot, or frame to the next. Thehopping pattern can be pseudo-random. The hopping pattern in frequencycan be predetermined and made known to both base stations and mobilestations explicitly or implicitly. The information about the hoppingpattern can also be embedded in the primary control signals. Forexample, information embedded in the current SYNC indicates thesubcarrier index q for the SYNC in next subframe, slot, or frame.

In some embodiments, the OFDM symbol that is used to transmit a primarycontrol signal or primary control signals may be divided into multiple(N) non-overlapping subbands in frequency, as depicted in FIG. 10. Thewidth of each subband is not necessarily equal, but may be sufficientlywide for a primary control signal. A primary control signal may occupythe entire subband or a section of the subband. In the latter case, theprimary control signal is not necessarily centered on the subband. Guardsubcarriers (zero energy) may be placed on both sides of the primarycontrol signal.

In other embodiments, multiple primary control signals can betransmitted in different subbands at the same time or in the same OFDMsymbol. In the example depicted in FIG. 11, multiple PSS may betransmitted using a set of subbands. In the next OFDM symbol, multipleSSS may be transmitted using the same set of subbands. Furthermore,multiple PBCH may be transmitted using the same set of subbands in otherOFDM symbols. In the event that the same primary control signals aretransmitted using multiple subbands in the same OFDM symbols, thereceived signals over these subbands can be combined in the frequencydomain at the receiver using a specific combining technique (e.g.,Maximum Ratio Combining) to process primary control signal.

Various subband configurations can be employed for transmission. In someembodiments, subbands may be assigned a priority for transmission ofprimary control signals so that a mobile may carry out search over thehigh-priority subbands first. The priority order can be predeterminedand made known to both base stations and mobile stations. The priorityorder can be pseudo-random or follow a natural pattern. For example,subband priority may descend from center to either end of the operationband. A mobile station may search a primary control signal over thecenter subband first and if it fails to find the primary control signal,it may then search over the subbands next to the center subband.

In other embodiments, a subband with a sufficient level of channelquality (e.g., sufficiently high mean SNR or sufficiently low averagelevel of interference) may be selected for primary control signaltransmission. Subband channel quality can be determined using variousmethods. For example, in a FDD system, mobile stations may survey thechannel quality of different subbands based on DL signals from theirserving base stations and feed the relevant information back to theirserving base stations, which then aggregate the information to determinethe subbands with a sufficient level of channel quality. In a TDDsystem, base stations may survey the channel quality of differentsubbands based on UL signals from their mobile stations and determinethe subbands with the a sufficient level of channel quality.

In further embodiments, primary control signals may be transmitted oversubband i in a subframe (or slot or frame) and over subband j in thenext subframe (slot or frame); that is, the transmission of primarycontrol signals hops from one subband to the other over time. Thehopping pattern can be pseudo-random or follow a natural pattern (e.g.,round robin). The hopping pattern can be predetermined and made known toboth base stations and mobile stations explicitly or implicitly. Theinformation about the hopping pattern can also be embedded in theprimary control signals. For example, information embedded in thecurrent SYNC indicates which subband the next SYNC will be transmittedover. Alternatively, a mobile station can carry out blind detection ofthe primary control signal.

A SYNC is a sequence in either time or frequency domain. Systeminformation can be embedded in the sequence. In particular, the n^(th)element of the sequence can be expressed as a function of

d(n)=f(n, I _(cell) , I _(subf) , q)

where I_(cell) denotes the cell identity, I_(subf) denotes the subframeindex, and q denotes the subcarrier index for the center subcarrier ofthe SYNC.

A PBCH carries system control information. In some embodiments, PBCH mayalso used to carry information to indicate usable (or unusable)frequency resources within the operation band. Frequency resources maybe organized as subcarriers, Resource Blocks (RB) of subcarriers, macroRB's, or subbands. In an embodiment, a PBCH may contain a bitmap that isused to indicate which frequency resources are usable or unusable, withbit value 1 signifying usable and 0 signifying unusable as depicted inFIG. 12. Such a bitmap can be further compressed using a particularcompressing method (e.g., run-length coding). Two bitmaps may be used:one for DL and the other for UL. In another embodiment, the PBCH maycontain two bit-fields that are used to indicate the unusable frequencyresources: one denoting the starting subcarrier (or block) index and theother denoting the ending subcarrier (or block).

To reduce overhead for indicating frequency resources within anoperating bandwidth, the system may define a frequency resource unit oflarge granularity (e.g., a macro RB (MRB)) that contains a plurality ofconsecutive frequency resource units of smaller granularity (e.g., RB's)and a message/bitmap in the PBCH may indicate the usable/unusable unitsof large granularity, instead of units of smaller granularity.

In other embodiments, regular control channels may be used to carryinformation to indicate usable (or unusable) frequency resources withinthe operating band. A regular control channel may contain downlinkcontrol information indicating the scheduled frequency resources fordownlink data transmission. Another regular control channel may containadditional control information indicating the scheduled frequencyresources for uplink data transmission. In the control signals/messages,the scheduled frequency resources (subcarriers, RB's, MRB's, orsubbands) for downlink or uplink transmission may only include theusable the usable frequency resources, which may be addressed or indexedas if the operation band is contiguous with only usable frequencyresources.

An indication of usable (unusable) frequency resources allow mobilestations to measure channel quality indications such as power level orsignal-to-interference-plus-noise ratio (SINR) over the usable frequencyresources. In addition, mobile stations may use the received signalswithin usable frequency resources for signal processing such asfrequency offset estimation. However, a base station or the system maysignal, via a PBCH, a regular control channel, or a control message in adata channel, a mobile station to monitor and measure the channelquality of the unusable frequency resources. A mobile station may alsoelect to monitor and measure the channel quality of unused frequencyresources as indicated by PBCH. The mobile station may then feed thechannel quality information back to the base station so that the basestation or system can make further decisions on the quality/usability ofthese frequency resources.

In some embodiments, the control server may determine center frequenciesor assigns subband for primary control signals based on the availableinterference information. The interference information can be obtainedusing different methods. In an embodiment, mobile stations may detectand measure interference that they experience, and send the interferenceinformation (e.g., its relative or absolute strength, its location infrequency, and its bandwidth) to their serving base stations. In anotherembodiment, the interference information may be derived from a databasethat is maintained by the system. The database may containgeo-locations, frequencies, and power levels of broadcast transmitters(e.g., high-power TV stations). The database may also containinterference information including frequency location and the strengthof the interference in one or more cells and in the vicinity of thenetwork generating through site surveys. A control server or a basestation may consult with the database so that it can determine a centerfrequency or subband for transmitting a primary control signal in orderto avoid strong interference from inter-system interferers. In addition,the server may coordinate the use of center frequencies or subbands byallocating a set of center frequencies or subbands to a cell for primarycontrol signals and a different set to its neighboring cell.Alternatively, base stations of neighboring cells exchange, via abackbone network (e.g., X2 Interface), the information on centerfrequencies or subbands they intend to use for their primary controlsignals. For example, base stations of neighboring cells exchange theSYNC and PBCH information (e.g., the time and/or frequency locations)and/or channels and information about usable/unusable frequencyresources (e.g., subcarriers, RB's, MRB's, or subbands) for data orcontrol channels/signals within the operation bandwidth through backbonenetwork (e.g., X2 Interface). In addition to exchanging aforementionedinformation, base stations of neighboring cells may send advertisementmessages about part or all of the aforementioned information to eachother, which then advertise the information regarding their neighbors toexpedite mobile station handoff, thereby reducing unnecessary overheadfor scanning in cell reselection.

In other embodiments, a base station may avoid using frequency resourcesunder severe interference for transmission of DL control channels (e.g.,Physical Control Format Indicator Channel, Physical Dedicated ControlChannel, and Physical Hybrid ARQ Indicator Channel) and data channels.Similarly, mobile stations, based on the information disseminated on thePBCH (e.g., the bitmaps or bit fields) indicating the usable or unusablefrequency resources, may carry out detection of DL regular controlchannels and data channels over the usable frequency resources. A basestation may make a determination to transmit reference signals in unusedfrequency resources. For example, the base station may choose totransmit reference signals within unused frequency resources for the useby mobiles (e.g., SINR estimation) or not to transmit reference signalswithin unused frequency resources. Similarly, a mobile station maychoose to use the reference signals within unused frequency resources ornot to. Furthermore, base stations may make frequency resources undersevere interference unavailable for the use of random access by mobilestations.

In further embodiments, base stations of cells in a single frequencynetwork (SFN) may only transmit SFN signals using the usable frequencyresources that are common to these cells. These base stations may send,via a backbone network, the information on the usable frequencyresources in their own cells to a server and the server may determinethe commonly usable frequency resources for SFN transmission among thesecells. The base stations may also exchange, via a backbone network, theinformation on the usable frequency resources in their own cells anddetermine among themselves the commonly usable frequency resources forSFN transmission. The frequency resources usable in a specific cell butnot usable in other SFN cells may be used for cell specific transmissionin that cell, such as cell-specific retransmission of the SFN signal. Abase station may use a signaling method (e.g., a bitmap) on a PBCH orother regular control channels to indicate unusable frequency resources,cell-specific frequency resources, or SFN frequency resources.Correspondingly, mobile stations may use the appropriate signaldetection and processing method to deal with the SFN frequency resourcesand cell-specific frequency resources.

A primary control signal may carry timing, frequency, location, systemparameter information, which enables a mobile station to find the basestation of the cell it is in, to synchronize with the network, and toaccess the network. In cell search procedures or cell reselectionprocedures for handoff, one of the steps is to detect the SYNC. In theevent that there are PSS and SSS, a mobile station may detect PSS firstand then SSS.

In some embodiments, the signal processor may process the receivedsignals with the following process, as shown in FIG. 13( a):

-   -   1. Frequency shift: the received signal is shifted in frequency        to multiplying a time varying complex factor e^(−j2πf) ^(c)        ^(t), where f_(c) is the possible frequency location of the        center subcarrier of the SYNC.    -   2. Low-pass filtering: A low-pass filter (LPF) is applied to the        frequency-shifted signals, where the bandwidth of the filter        corresponds to the bandwidth of the SYNC signal.    -   3. Correlation: Correlation is carried out between the filtered        signals and the time-domain sequence of the SYNC with its center        subcarrier at DC (direct current), which is called unshifted        sequence here.    -   4. Peak detection: A peak detector is used to determine if a        SYNC is detected.

In other embodiments, the signal processor may process the receivedsignals with the following process, as shown in FIG. 13( b):

-   -   1. Band-pass filtering: A band-pass filter (BPF) is applied to        the received signals, where the bandwidth of the filter        corresponds to the bandwidth of the SYNC signal and the center        of the pass band is the possible frequency location of the        center subcarrier of the SYNC, f_(c).    -   2. Correlation: Correlation is carried out between the filter        signals and the time-domain sequence of the SYNC with its center        subcarrier at f_(c), which is called shifted sequence here.    -   3. Peak detection: A peak detector is used to determine if a        SYNC is detected.

If f_(c) is known to the mobile station, either process may be repeateduntil a SYNC is detected. If f_(c) is unknown to the mobile, eitherprocess can be repeated sequentially for each possible center subcarrierlocation f_(c) until a SYNC is detected. Alternatively, either processcan be carried out concurrently for all possible center subcarrierlocations; that is, there are multiple (N) parallel paths for detectingthe SYNC, each one for a possible center subcarrier location f_(c)(n),as shown in FIG. 14.

The above processes can be implemented using software, firmware, orhardware.

The above detailed description of embodiments of the system is notintended to be exhaustive or to limit the system to the precise formdisclosed above. While specific embodiments of, and examples for, thesystem are described above for illustrative purposes, various equivalentmodifications are possible within the scope of the system, as thoseskilled in the relevant art will recognize. For example, while processesare presented in a given order, alternative embodiments may performroutines having steps in a different order, and some processes may bedeleted, moved, added, subdivided, combined, and/or modified to providealternative or subcombinations. Each of these processes may beimplemented in a variety of different ways. Further any specific numbersnoted herein are only examples: alternative implementations may employdiffering values or ranges.

These and other changes can be made to the invention in light of theabove Detailed Description. While the above description describescertain embodiments of the technology, and describes the best modecontemplated, no matter how detailed the above appears in text, theinvention can be practiced in many ways. Details of the system may varyconsiderably in its implementation details, while still beingencompassed by the technology disclosed herein. As noted above,particular terminology used when describing certain features or aspectsof the technology should not be taken to imply that the terminology isbeing redefined herein to be restricted to any specific characteristics,features, or aspects of the technology with which that terminology isassociated. In general, the terms used in the following claims shouldnot be construed to limit the invention to the specific embodimentsdisclosed in the specification, unless the above Detailed Descriptionsection explicitly defines such terms. Accordingly, the actual scope ofthe invention encompasses not only the disclosed embodiments, but alsoall equivalent ways of practicing or implementing the invention underthe claims.

FIG. 15 depicts an exemplary operational procedure for communication viaan operating frequency channel by a base station in a multi-carriercommunications system including operations 1500, 1502, and 1504. In oneembodiment, the multi-carrier communications system comprises aplurality of base stations and mobile stations, the base station servinga cell among a plurality of cells.

Referring to FIG. 15, operation 1500 begins the operational procedureand in operation 1502 a specific primary control channel selected. Inone embodiment, the specific primary control channel is selected fromamong multiple primary control channels at distinct center frequencylocations within the operating frequency channel. In some embodiments,each of the multiple primary control channels is characterized by beingcapable of carrying a primary control signal, having a number ofcontiguous subcarriers, and having a bandwidth substantially narrowerthan a bandwidth of the operating frequency channel. Additionally andoptionally, the specific primary control channel is different from atleast one of the multiple primary control channels selected by at leastone other base station in the system.

In operation 1504, a primary control signal is generated. In oneembodiment, the primary control signal is generated by modulating asequence on subcarriers of the specific primary control channel. In someembodiments, the sequence has an autocorrelation with a high correlationpeak with respect to sidelobes. Furthermore, the sequence may containinformation on cell identity. Additionally and optionally, the primarycontrol signal has a small peak-to-average power ratio.

In operation 1506, the primary control signal is broadcasted to mobilestations within the cell.

In some embodiments, the specific primary control signal enables amobile station within the cell to perform initial synchronization withthe base station in time or frequency.

In one embodiment, the specific primary control signal is modulated inan orthogonal frequency division multiplexing (OFDM) symbol.

In an embodiment, the sequence is a binary sequence. In otherembodiments, the sequence is a non-binary sequence. In furtherembodiments, the sequence is a Zadoff-Chu sequence.

In one embodiment, the primary control signal has a smallpeak-to-average power ratio in the time domain.

In some embodiments, information of the center frequency location of thespecific primary control channel is sent to other base stations in thesystem via a network connecting the plurality of base stations.

In some embodiments, the base station broadcasts to mobile stationswithin the cell the frequency locations of the primary control channelsused in other cells in the system.

In some embodiments, a control signal is broadcast, indicating frequencyresources usable for communication between the base station and mobilestations within the cell.

In some embodiments, a bitmap is used to indicate usable subbands withinthe operating frequency channel.

In some embodiments, the selection of the specific primary controlchannel is based on operational conditions of the multiple primarycontrol channels. The operational conditions may be related tointerference level or signal-to-noise ratio. In other embodiments, theselection of the specific primary control channel varies from onesubframe, slot, or frame to the next. In some embodiments, the selectionof the specific primary control channel is based on a frequency usageschedule.

In some embodiments, another primary control signal is transmitted onanother primary control channel.

In some embodiments, another specific primary control channel isselected from among the multiple primary control channels, anotherprimary control signal is generated by modulating another sequence onsubcarriers of the another specific primary control channel, and thisprimary control signal is broadcast to the mobile stations within thecell.

FIG. 16 depicts an exemplary operational procedure for communication viaan operating frequency channel by a mobile station in a multi-carriercommunications system comprising a plurality of base stations and mobilestations including operations 1600, 1602, and 1604.

Referring to FIG. 16, operation 1600 begins the operational procedureand in operation 1602 detecting a primary control signal transmittedfrom a base station serving a cell in the system. In one embodiment,this is done by searching over multiple primary control channels atdistinct center frequency locations within the operating frequencychannel. In one embodiment, each of the multiple primary controlchannels is characterized as having a number of contiguous subcarriersand a bandwidth substantially narrower than a bandwidth of the operatingfrequency channel. In another embodiment, the primary control signalcomprises a sequence modulating on subcarriers of a primary controlchannel. Furthermore, the sequence may have an autocorrelation with alarge correlation peak with respect to sidelobes. Additionally andoptionally, the sequence may contain cell identity information. In someembodiments, the primary control signal may have a small peak-to-averagepower ratio.

In operation 1604, time or frequency synchronization is performed basedon the detected primary control signal.

In one embodiment, a correlation is performed between the receivedsignal and a sequence stored at the mobile device. In an embodiment,symbol time acquisition is performed. In another embodiment, cellidentity detection is performed. In another embodiment, frame boundarydetection is performed. In another embodiment, information decoding isperformed on a physical broadcasting channel (PBCH).

In one embodiment, an interference measurement is performed. In anotherembodiment, a neighbor advertisement message is received containinginformation on center frequency locations of primary control channelsused in neighboring cells. In another embodiment, a handover procedureis performed.

Any of the above mentioned aspects can be implemented in methods,systems, computer readable media, or any type of manufacture. Forexample, a computer readable medium can store thereon computerexecutable instructions for communicating in a wireless communicationssystem.

Lastly, while the present disclosure has been described in connectionwith the preferred aspects, as illustrated in the various figures, it isunderstood that other similar aspects may be used or modifications andadditions may be made to the described aspects for performing the samefunction of the present disclosure without deviating there from. Forexample, in various aspects of the disclosure, methods and systems forcommunicating in a wireless communications system were disclosed.However, other equivalent mechanisms to these described aspects are alsocontemplated by the teachings herein. Therefore, the present disclosureshould not be limited to any single aspect, but rather construed inbreadth and scope in accordance with the appended claims.

1. A method for communication via an operating frequency channel by abase station in a multi-carrier communications system comprising aplurality of base stations and mobile stations, the base station servinga cell among a plurality of cells, the method comprising: selecting aspecific primary control channel among multiple primary control channelsat distinct center frequency locations within the operating frequencychannel, wherein: each of the multiple primary control channels ischaracterized by being capable of carrying a primary control signal,having a number of contiguous subcarriers, and having a bandwidthsubstantially narrower than a bandwidth of the operating frequencychannel; and the specific primary control channel is different from atleast one primary control channel selected by at least one other basestation in the system; generating a primary control signal by modulatinga sequence on subcarriers of the specific primary control channel,wherein: the sequence has an autocorrelation with a large correlationpeak with respect to sidelobes; the sequence contains information oncell identity; and the primary control signal has a smallpeak-to-average power ratio; and broadcasting the primary control signalto mobile stations within the cell.
 2. The method of claim 1, whereinthe specific primary control signal enables a mobile station within thecell to perform initial synchronization with the base station in time orfrequency.
 3. The method of claim 1, wherein the specific primarycontrol signal is modulated in an orthogonal frequency divisionmultiplexing (OFDM) symbol.
 4. The method of claim 1, wherein thesequence is a binary sequence.
 5. The method of claim 1, wherein thesequence is a non-binary sequence.
 6. The method of claim 1, wherein thesequence is a Zadoff-Chu sequence.
 7. The method of claim 1, wherein theprimary control signal has a small peak-to-average power ratio in thetime domain.
 8. The method of claim 1, wherein information of the centerfrequency location of the specific primary control channel is sent toother base stations in the system via a network connecting the pluralityof base stations.
 9. The method of claim 1, further comprisingbroadcasting, by the base station to mobile stations within the cell,the center frequency locations of the primary control channels used inother cells in the system.
 10. The method of claim 1, further comprisingbroadcasting a control signal indicating frequency resources usable forcommunication between the base station and mobile stations within thecell.
 11. The method of claim 7, further comprising using a bitmap toindicate usable subbands within the operating frequency channel.
 12. Themethod of claim 1, wherein the selection of the specific primary controlchannel is based on operational conditions of the multiple primarycontrol channels.
 13. The method of claim 12, wherein the operationalconditions are related to interference level or signal-to-noise ratio.14. The method of claim 1, wherein the selection of the specific primarycontrol channel varies from one subframe, slot, or frame to the next.15. The method of claim 1, further comprising transmitting anotherprimary control signal on another primary control channel.
 16. Themethod of claim 1, wherein the selection of the specific primary controlchannel is based on a frequency usage schedule.
 17. The method of claim1, further comprising selecting another specific primary control channelamong the multiple primary control channels, generating another primarycontrol signal by modulating another sequence on subcarriers of theanother specific primary control channel, and broadcasting the anotherprimary control signal to the mobile stations within the cell.
 18. Abase station configured to communicate via an operating frequencychannel in a multi-carrier communications system comprising a pluralityof base stations and mobile stations, the base station serving a cellamong a plurality of cells, the base station comprising: a computingdevice comprising at least one processor; and a memory communicativelycoupled to said processor when the base station is operational; thememory having stored therein computer instructions that upon executionby the at least one processor cause: selecting a specific primarycontrol channel among multiple primary control channels at distinctcenter frequency locations within the operating frequency channel,wherein: each of the multiple primary control channels is characterizedby being capable of carrying a primary control signal, having a numberof contiguous subcarriers, and having a bandwidth substantially narrowerthan a bandwidth of the operating frequency channel; and the specificprimary control channel is different from at least one primary controlchannel selected by at least one other base station in the system withinthe operating frequency channel; generating a primary control signal bymodulating a sequence on subcarriers of the selected primary controlchannel, wherein: the sequence has an autocorrelation with a largecorrelation peak with respect to sidelobes; the sequence carries cellidentity information; and the primary control signal has a smallpeak-to-average power ratio; and broadcasting the primary control signalto mobile stations within the cell.
 19. A computer readable storagemedium storing thereon computer executable instructions forcommunication via an operating frequency channel by a base station in amulti-carrier communications system comprising a plurality of basestations and mobile stations, the base station serving a cell among aplurality of cells, the computer readable storage medium comprising:instructions for selecting a specific primary control channel amongmultiple primary control channels at distinct center frequency locationswithin the operating frequency channel, wherein: each of the multipleprimary control channels is characterized by being capable of carrying aprimary control signal, having a number of contiguous subcarriers, andhaving a bandwidth substantially narrower than a bandwidth of theoperating frequency channel; and the specific primary control channel isdifferent from at least one primary control channel selected by at leastone other base station in the system within the operating frequencychannel; instructions for generating a primary control signal bymodulating a sequence on subcarriers of the selected primary controlchannel, wherein: the sequence has an autocorrelation with a largecorrelation peak with respect to sidelobes; the sequence contains cellidentity information; and the primary control signal has a smallpeak-to-average power ratio; and instructions for broadcasting theprimary control signal to mobile stations within the cell.
 20. A methodfor communication via an operating frequency channel by a base stationin a multi-carrier communications system comprising a plurality of basestations and mobile stations, the base station serving a cell among aplurality of cells, the method comprising: selecting a specific primarycontrol channel among multiple primary control channels at distinctcenter frequency locations within the operating frequency channel,wherein: each of the multiple primary control channels is characterizedby being capable of carrying a primary control signal, having a numberof contiguous subcarriers, and having a bandwidth substantially narrowerthan a bandwidth of the operating frequency channel; and the specificprimary control channel is different from at least one primary controlchannel selected by at least one other base station in the system withinthe operating frequency channel; generating a primary control signal bymodulating a Zadoff-Chu sequence on subcarriers of the selected primarycontrol channel; and broadcasting the primary control signal to mobilestations within the cell.
 21. A method for communication via anoperating frequency channel by a mobile station in a multi-carriercommunications system comprising a plurality of base stations and mobilestations, the method comprising: detecting, by searching over multipleprimary control channels at distinct center frequency locations withinthe operating frequency channel, a primary control signal transmittedfrom a base station serving a cell in the system, wherein: each of themultiple primary control channels is characterized by having a number ofcontiguous subcarriers and a bandwidth substantially narrower than abandwidth of the operating frequency channel; and the primary controlsignal comprises a sequence modulating on subcarriers of a primarycontrol channel, wherein: the sequence has an autocorrelation with alarge correlation peak with respect to sidelobes; the sequence containscell identity information; and the primary control signal has a smallpeak-to-average power ratio; and performing time or frequencysynchronization based on the detected primary control signal.
 22. Themethod of claim 21, further comprising performing a correlation betweenthe received signal and a sequence stored at the mobile device.
 23. Themethod of claim 21, further comprising performing symbol timeacquisition.
 24. The method of claim 21, further comprising performingcell identity detection.
 25. The method of claim 21, further comprisingperforming frame boundary detection.
 26. The method of claim 21, furthercomprising performing information decoding on a physical broadcastingchannel (PBCH).
 27. The method of claim 21, further comprisingperforming an interference measurement.
 28. The method of claim 21,further comprising receiving neighbor advertisement message containinginformation on center frequency locations of primary control channelsused in neighboring cells.
 29. The method of claim 21, furthercomprising performing a handover procedure.
 30. A mobile deviceconfigured to communicate via an operating frequency channel in amulti-carrier communications system comprising a plurality of basestations and mobile stations, the mobile device comprising: at least oneprocessor; and a memory communicatively coupled to said processor whenthe mobile device is operational, the memory having stored thereincomputer instructions that upon execution by the at least one processorcause: detecting, by searching over multiple primary control channels atdistinct center frequency locations within the operating frequencychannel, a primary control signal transmitted from a base stationserving a cell in the system, wherein: each of the multiple primarycontrol channels is characterized by having a number of contiguoussubcarriers and a bandwidth substantially narrower than a bandwidth ofthe operating frequency channel; the primary control signal comprises asequence modulating on subcarriers of a primary control channel,wherein: the sequence has an autocorrelation with a large correlationpeak with respect to sidelobes; the sequence contains cell identityinformation; and the primary control signal has a small peak-to-averagepower ratio; and performing time or frequency synchronization based onthe detected primary control signal.
 31. A method for communication viaan operating frequency channel by a mobile station in a multi-carriercommunications system comprising a plurality of base stations and mobilestations, the method comprising: detecting, by searching over multipleprimary control channels at distinct center frequency locations withinthe operating frequency channel, a primary control signal transmittedfrom a base station serving a cell in the system, wherein: each of themultiple primary control channels is characterized by having a number ofcontiguous subcarriers and a bandwidth substantially narrower than abandwidth of the operating frequency channel; the primary control signalcomprises a Zadoff-Chu sequence modulated on subcarriers of a primarycontrol channel; and the Zadoff-Chu sequence contains cell identityinformation; performing time or frequency synchronization based on thedetected primary control signal.